[reaction: see text] The activity of the complex (IPr)PdCl(eta2-N,C-C12H7NMe2), 1 [IPr = (N,N'-bis(2,6-diisopropylphenyl)imidazol)-2-ylidene], in the Suzuki-Miyaura cross-coupling reaction involving unactivated aryl chlorides and triflates with arylboronic acids at room temperature in technical grade 2-propanol is described. These conditions allow for the synthesis of di- and tri-ortho-substituted biaryls in very short reaction times. This complex also displays very high activity for alpha-ketone arylation and dehalogenation reactions of activated and unactivated aryl chlorides.
Zweifach: Die Titelmethode liefert Arylvinylether in hohen Ausbeuten, in kurzer Reaktionszeit, mit Z‐Stereospezifität und guten Regioselektivitäten. Einblicke in den Reaktionsmechanismus betonen die Rolle von [{Au(NHC)}2(μ‐OH)][BF4] (NHC=N‐heterocyclisches Carben) als Lewis‐Säure [Au(NHC)][BF4] und als Brønsted‐Base [Au(NHC)(OH)] – zwei Goldeinheiten, die synergistisch wirken.
The synthesis of a series of digold hydroxide complexes is reported. These diaurated species, of the formula [{Au(NHC)} 2 (μ-OH)][BF 4 ] (where NHC = IPr Cl , IPr*, IPent), were easily prepared via the cationic species [Au(NHC)-(NCCH 3 )][BF 4 ] in aqueous media. The catalytic activity of these novel complexes was tested and compared to that of the previously reported IPr and SIPr derivatives. These digold hydroxide species are highly active in water-inclusive organic transformations, such as the alkyne and nitrile hydration reactions, and the Meyer−Schuster rearrangement. One salient feature of these systems is the lack of any additive to induce catalytic activity.
Nickel(0)-catalyzed asymmetric three-component coupling of 1,3-dienes, aldehydes, and silanes has been realized utilizing a chiral N-heterocyclic carbene as a ligand. On the basis of the screening of various NHC precursors, an imidazolium salt having 1-(2,4,6-trimethylphenyl)propyl groups on the nitrogen was designed and synthesized. In this reaction, various coupling products were produced in good yields with high regio-, diastereo- (anti selective in the case of the internal 1,3-diene), and enantioselectivities (up to 97% ee).
Herein, we present a detailed investigation of the mechanistic aspects of the dual gold-catalysed hydrophenoxylation of alkynes by both experimental and computational methods. The dissociation of [{Au(NHC)}2 (μ-OH)][BF4 ] is essential to enter the catalytic cycle, and this step is favoured by the presence of bulky, non-coordinating counter ions. Moreover, in silico studies confirmed that phenol does not only act as a reactant, but also as a co-catalyst, lowering the energy barriers of several transition states. A gem-diaurated species might form during the reaction, but this lies deep within a potential energy well, and is likely to be an "off-cycle" rather than an "in-cycle" intermediate.
The total synthesis of (–)‐corynantheidine has been achieved through Ni0‐mediated carboxylative cyclization as the key reaction step with incorporation of CO2, and this cyclization was also successfully expanded to the catalytic reaction by using Et2Zn in the presence of an excess amount of DBU.
Giving direction: An C sp 3-H bond activation directed by a rhodacycle intermediate has been found to occur in a Rh(I)-catalyzed reaction between an allene moiety having a tert-butyl substituent, and tethered alkynes. Cyclic compounds containing a cyclopropane ring were obtained in good to high yields (up to 92%).
Rh(I)-catalyzed formal [6 + 2] cycloaddition of allenal 6 having an alkyne or alkene in a tether proceeded smoothly, giving 5-8- and 6-8-fused bicyclic ketone derivatives 7 in good to excellent yields. It was also found that cyclization of enantiomerically enriched (S)-6a (94% ee) gave cyclic ketone derivative (S)-7a in high yield with reasonable chirality transfer (86% ee). This result indicates that this cyclization proceeds through stereoselective formation of rhodacycle H' followed by insertion of a multiple bond.
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